Shaken not sturdy

It was billed as a symbol of British mastery of design and technology but wound up being a national embarrassment. So was London's wobbly bridge a product of over-ambitious 'emotional' design or flawed engineering? And why didn't anyone think of testing it? Andy Beckett investigates
Special report: the millennium

If you go down to the millennium bridge in London, after midnight, when the workmen are gone and the buildings around are silent and darkened, you may notice something surprising. At the south end, behind the builders' hoardings, a solitary security guard sits in a steamed-up Portakabin. He'll be there for as long as it takes the bridge's wobbles to be cured. At the north end there are some temporary gates, locked but not that tall, a piece of paper pinned up reading "Bridge Closed", the pins already old-looking and rusted, and a single word of graffiti: "Why?".

And beyond the gates, out over the black Thames, between the swooping, lit-up handrails of Britain's most currently infamous architectural experiment, there may be silhouettes moving about - illicit visitors: curious people testing the decking, couples smoking cigarettes in midstream, people just marvelling at the views and taut steel. "You feel suspended in space above the river," says one. "It was a sublime experience." After watching the moon and the skyline for a while, he walked back towards the riverbank: "I saw another dozen people climbing up."

Even by British standards, the bridge has become an ambiguous piece of modern architecture. It has been shut for more than a month, ever since 200,000 people - about five times the number expected - turned up on its opening weekend. A campaign to re-open it, before the vibrations are even dampened, is gaining momentum in the London Evening Standard.

In some ways, this slim, silvery span and the appetite for using it seem to demonstrate a new national confidence in all things hi-tech and streamlined. Ever since its construction was announced five years ago, the bridge has been talked about excitedly in science fiction terms: a "blade of light", a "magic carpet", an "absolute statement", in the words of its designers Foster and Partners, "of our capabilities at the beginning of the 21st century".

New bridges in general, after decades as unloved and ugly projects, are back in fashion. There are plans for more in London. There are millennium crossings underway or recently completed in York, Peterborough, Tyneside and County Fermanagh. These arcs of glass and aluminium seem to offer spectacle and usefulness, opportunities for regeneration and property development, publicity for their surrounding areas - the perfect combination, it appears, for the contemporary urban planner. Mark Whitby, a bridge engineer with three British projects on the go, says local councils now tend to choose the "most adventurous" design on offer.

But what if it wobbles? When the millennium bridge's wide deck began to buck and sway, all this adventure suddenly looked slightly reckless. Aesthetics - one of the bridge's engineers approvingly described its design as "emotional not rational" - seemed to have overwhelmed practicality. And as identifying the precise problem, and its origin, and how to solve it, has lengthened the likely closure from "a few weeks" to "a few months" to "a matter of months - hopefully", so the structure has started to become a British symbol of a more traditional sort: a big project running late.

At first, official statements about the bridge, like an an untrustworthy station announcer's, see-sawed between evasion, over-confidence, and sulkiness. It was the pedestrians' fault. Or it was strictly the bridge engineers' (Foster and Partners remain keen to redirect press enquiries to Ove Arup). Or there was no problem at all, just a national suspicion of "ambition". Lately, the PR line has softened: "The swaying is bridge-induced, not pedestrian- induced," admits Tony Fitzpatrick, Arup's bridge overseer. He says that a solution - flexible shock absorbers fixed along the underside - is currently being discussed with the relevant manufacturers. But the anxiety set off by the bridge, and the over-budget Jubilee Line, and the late-starting millennium wheel, and the deflating Millennium Dome, and the builder-blighted quality of British cities in general, remains. Must building ambitiously in Britain always be such a struggle?

According to the official history of the millennium bridge project, the publication of which has also been delayed, a crossing between Southwark and St Paul's Cathedral was first suggested in 1851. It took another 60 years before an Act of Parliament was passed to authorise it, and another three were spent discussing whether the bridge should be positioned to create a new tram route or give the best possible view of St Paul's. Finally, in 1914, a florid classical design was chosen which included "a winged goddess driving a two-horse chariot". Then the first world war broke out.

The idea of a link between the prosperous City and poor south London gradually faded, as idealistic schemes for the capital tend to. It took the re-awakening of interest in grand architectural gestures along the Thames during the 90s to revive the bridge-building notion. David Bell, now chairman of the Millennium Bridge Trust, was working for the Financial Times in Southwark: "My office overlooked the river. I thought, 'Wouldn't it be fantastic to build a bridge from St Paul's to the Bankside power station?'"

Bankside was already marked for conversion into the Tate Modern. Southwark council was keen to make a cultural quarter out of its concrete flatlands. Tourism on both riverbanks would clearly benefit. But Bell was quickly made aware that such arguments might not be sufficient. "Everybody said, 'You'll never get permission.'"

He decided to use publicity as a weapon. In 1996, the Financial Times sponsored a public competition asking architects, engineers and artists to devise a crossing. More than 200 designs were submitted; one of them was from Foster and Partners, Ove Arup, and the veteran British sculptor Sir Anthony Caro. Precisely which of them initiated this collaboration is now a matter of polite jockeying. Caro says he called Foster. Ken Shuttleworth, the Foster partner in charge of the bridge, says they were thinking about entering anyway. Chris Wise, the Arup engineer most involved early on, has now left the company and communicates via cryptic phone messages.

What seems fairly certain is that, one evening that summer, Wise and a fellow Arup engineer, having agreed to meet Foster and Shuttleworth and Caro the next morning, went to a wine bar called Zelda's in Charlotte Street in central London and started drawing on napkins. They steadily rejected conventional designs - a suspension bridge's towers, for example, would have obscured St Paul's - for a flat, minimal platform "stretched as tightly as possible between the two banks", as Wise put it later. "We went home that night tremendously excited about the purity of the diagram, and petrified that the bridge might shake itself to bits..."

The following morning, they gathered at Caro's studio up the road in Camden. While Caro's assistants made rough cardboard models, Wise's "guitar string" design evolved into the "blade of light" Foster envisaged. Sitting in the studio's low, boxy chairs, surrounded by bold frag ments of recent Caro projects, they did not dwell too much, at least as the meeting is remembered, on the more prosaic question of the bridge shaking.

In December 1996, their design was announced the winner. "And I thought that was what you built," says Caro, ruefully creasing his brow. "How naive I was." For the next two and a half years, during many meetings at Foster and Partners, and impromptu group expeditions to the riverbanks, and an eternity of discussions with planning authorities, the actual structure of the bridge was determined. There were compromises: the flat span became a less abrupt arch, Caro's plans for elaborate ramps and gateways at either end were watered down. There were endless explanations: some sceptics in the City demanded to know how the bridge's lights could be kept free of charred insects. And, on occasions, there was a sense close to futility: when Foster gave a presentation to a City planning committee, the first ever by an architect, the first questioner afterwards thanked "Sir Richard Rogers".

But Foster, unlike Caro, was used to the minefield of a public commission. At one stage, the architects successfully re-submitted some rejected drawings by making the sky bluer and the bridge users younger. "What Nor man absolutely correctly judged," says Fitzpatrick, slipping easily into a public relations abstraction, "was generating the sense of wonderment".

Ove Arup gave the bridge its highest rating for complexity of construction - the same as a state-of-the-art corporate fortress. The cost, met by Southwark, the City, business donors and, most of all, the millennium commission, rose from around £10m to approaching £20m as the committees nit-picked and the Thames harassed the workmen. Building took 13 months instead of the promised 12; at the official opening in April, the Queen could only edge halfway across. Even now, behind the hoardings at the south end, the promised landscaping is piles of wet gravel and an abandoned wheelbarrow.

Since the bridge closed, there has been a suspicion that contemporary engineers are perhaps getting a bit carried away. The construction of models on computer screens, and the convergence of architecture and engineering have "released the engineer", says Whitby, "from the need to prove absolutely he knows what he's doing". He thinks this is good - experiment and the passing problems that result are the best way to learn more. The bridge's spin doctors have been arguing the same in recent weeks.

But another engineer, more closely involved with the millennium scheme, disagrees. "There's got to be tremendous care when a competition goes ahead that the engineering is sound," he says. He suggests that the judges in this case, who included politicians, businessmen from non-architectural fields, and the broadcaster Anna Ford, were more concerned with the look of the crossing, and the attendant possibilities for publicity, than with its structural soundness. "I was concerned about vibration when I first saw the plans over two years ago," he says.

Fitzpatrick responds that every possible test was done. A Canadian wind tunnel was hired to imitate gusts off the Thames, for example, before the bridge had even been commissioned. What about testing the span with crowds of people? There is an uncharacteristic pause. "Load testing of a new design is extremely rare. Bridges are built to the codes developed by the great and the good... They are built well within factors of safety." He pauses again. "The only way to have picked this up would have been a false opening. And you can't use the public for that."

Last week, Bell offered me a bridge tour regardless. Rain was blasting up the Thames. He climbed a slippery, wet ladder in his pinstripe suit, clambered over some scaffolding onto the streaming deck, and attempted to explain the latest official position. "The millennium wheel had its problems, but people forgot about them very quickly," he half-bellowed, as we battered our way to midstream. The bridge bounced very lightly beneath our feet. On all sides, above the handrails, London loomed dripping and magnificent. He grinned winningly. The spine of the bridge curved upward. We might have been climbing into the sky.

But afterwards, in the Portakabin, a thought occurred. Would the water on the deck freeze in winter? "The maintenance people have that under control," said Bell. "Besides, things rarely freeze in London."